The seed is one of the most relevant inputs for a good initial performance of the soybean crop. It is necessary to know which factors can interfere in the production of the crop, the association between the size of the seeds in the germination and vigor has already been analyzed by many effective authors to prove its influence. The present research aimed to evaluate the seed size in the germination of the vigor and performance of soybean seedlings. The completely randomized design was used with 4 treatments (Classification in sieves 5; 6; 6.5 mm, and control without classification in the beneficiation). The germination, vigor by the First Count tests, tetrazolium, Emergency Speed Index-IVE and Seedling performance by root length and Seedling length are histories. It was concluded that, under the conditions in which the research was carried out, there was no influence of the size of the seed on germination. For the positivity vigor of the seed size, being that the bigger seeds lesser performance of the vigor for the testicles of accelerated aging and seedling length.